Alright everyone, I have posted this issue now about three times. Does anyone have a clue? Ok, this is the deal. I have a 91' 350 Tpi. Ok, the car runs rough after the engine warms up. It runs great when the engine is cold and runs really good if I have less than an eighth of a tank of gas , regrardless of weather or not the engine is warm or cold!! . When, I have more than an eighth of a tank it runs like ****. If I drive it hard just once , and when it has more than an eighth of a tank then shifting into second, third is sluggish. What I mean is the car feels like it is being held back or their is some kind of fuel blockage. I have replaced the following already: fuel press. regulator, fuel injectors, fuel filter, fuel cap, dist cap, rotor. I was told by a shop that it could be my locking gas cap I got at walmart! LOL. I tried taking off the fuel cap when I felt the trouble start and it seemed to help slightly. Maybe my fuel pump is dropping in voltage? and when the car is low on gas then maybe it runs better cause all cars are faster when they are about to run out of gas!!???? Some one please help. OH, and also when I turn on my electric fan switch manually and the car cools down it runs good again until it heats back up.